In some industrial vehicles such as a forklift, wet multiple disc brakes are adopted as a service brake and a parking brake of an axle. By adopting a wet multiple disc brake, the service life of the brake can be extended. Axles of this type are disclosed in, for example, Patent Literatures 1 and 2.
FIG. 4 is a partial sectional view of an axle of an industrial vehicle disclosed in Patent Literature 1. FIG. 5 is a view taken along the line A-A of FIG. 4. The axle comprises an axle housing 6, an axle shaft 60 inserted in the axle housing 6, and a frame support 61 arranged around an outer periphery of the axle shaft 60. An inner diameter portion of the frame support 61 is fixed to a flange portion 6a of the axle housing 6 with bolts 62, and an outer diameter portion of the frame support 61 is fixed to a frame 63 of the body with bolts 64.
A wheel hub 65 is arranged on the outer periphery of the axle housing 6 via bearings 66. One end of the wheel hub 65 is fixed to a flange end portion 60a of the axle shaft 60 with bolts 67, and the other end of the wheel hub 65 is fixed to a brake hub 68 and a rim 69 of a wheel with bolts 70. A brake cover 71 and a center cover 72 are fixed to the frame support 61 with bolts 73.
Friction plates 74 are engaged with splines of the brake hub 68 so as to be movable in the axial direction of the axle shaft 60. Mating plates 75 are engaged with splines of the center cover 72 so as to be movable in the axial direction of the axle shaft 60. The friction plates 74 and the mating plates 75 are alternately arranged in the axial direction of the axle shaft 60.
A parking piston 76 is arranged inside the frame support 61 so as to be movable in the axial direction of the axle shaft 60. Parking springs 77 are arranged between the parking piston 76 and the frame support 61. Service pistons 78 are housed in the frame support 61 so as to be movable in the axial direction of the axle shaft 60. As shown in FIG. 5, the service pistons 78 and the parking springs 77 are arranged in a circumferential direction around an axial center 600 of the axle shaft 60. An oil chamber 79 is provided for the parking piston 76. An oil chamber 80 is provided for each of the service pistons 78.
In order to operate the parking brake, an oil feeding/discharging device (not shown) discharges the hydraulic oil from each of the oil chambers 80 through an oil passage 81 and an outlet 82 (see FIG. 5), and discharges the hydraulic oil from the oil chamber 79 through an oil passage 83. Then, the parking piston 76 is pressed against both the plates 74 and 75 by the biasing force of the parking springs 77, and thereby the plates 74 and 75 are brought into pressure contact with each other. As a result, rotation of the wheel is blocked. In order to release the parking brake, the oil feeding/discharging device supplies the hydraulic oil to the oil chamber 79 through the oil passage 83 to move the parking piston 76 away from the plates 74 and 75 against the biasing force of the parking springs 77. Thereby, the pressure contact between the plates 74 and 75 is released.
In order to operate the service brake, the parking brake is released in advance as described above. The oil feeding/discharging device supplies the hydraulic oil to each of the oil chambers 80 through an inlet 84 (see FIG. 5) and the oil passage 81. Then, the service pistons 78 are pressed against the plates 74 and 75, and thereby the plates 74 and 75 are brought into pressure contact with each other. As a result, the wheel is braked.
As described above, in this axle, the parking brake and the service brake are integrated and share the friction plates 74 and the mating plates 75.